This invention relates to improvements in expanding dowels of the type used in accurately and repeatably locating a first part with respect to a second or reference part, and, more particularly, to a dowel having a tapered expansion pin slidably within an expandable sleeve such that the sleeve may be removably retained within aligned openings or holes provided in the parts in order to retain the parts assembled as a unit.
It is known to use expandable dowels to locate a first part or workpiece having a through hole relative to a second or reference part, for instance a fixture, having a locating hole. Commonly assigned U.S. Pat. No. 2,901,787 issued on Sep. 1, 1959 discloses a dowel having a generally cylindrical sleeve formed of resiliently deformable material and provided with a tapered axial bore and a slot extending the length of the sleeve wall to permit radial expansion and contraction of the sleeve. Once the sleeve has been inserted into axially aligned holes in the workpiece and reference part, an expansion pin having an outer surface tapered to complement the sleeve bore is driven into the sleeve bore, for instance by striking a punch engaged with an exposed end of the expansion pin with a hammer or mallet sufficiently to force an outer surface of the sleeve to expand into secure surface-to-surface frictional clamping engagement with inner surfaces of the holes to effect alignment of such holes and assembly of the workpiece and reference part as a unit.
Subsequent removal of the dowel is generally carried out in a two-step procedure. First, an internally threaded pull nut or extractor is screwed onto a threaded extension of the expansion pin sufficiently to successively seat the pull nut on an outer end of the sleeve and then to withdraw the expansion pin from the sleeve in order to allow the sleeve to contract. Second, the sleeve is removed from the holes, and where the hole in the reference part is a blind hole, it is necessary to use an insertable sleeve puller designed to hook into a recess in the sleeve to pull the sleeve from the holes.
There are several recognized disadvantages associated with prior art dowels of the type described above. Such dowels require a separate tool, i.e. the sleeve puller, for the second removal step to completely remove the dowel from a blind hole. Consequently, time must be expended by a machinist in locating a sleeve puller and using it to remove a sleeve or plurality of sleeves from the holes. A further disadvantage is that the uncoupled sleeve and expansion pin may easily become separated and misplaced from each other, resulting in additional time being spent by a user in finding a matching-sized sleeve and expansion pin.